Small cell lung cancer is a type of lung cancer that originates in the small air sacs (alveoli) of the lungs. It is one of two main types of lung cancer, with non-small cell lung cancer being the other type. Small cell lung cancer tends to spread quickly and often involves the hematogenous route through the bloodstream or lymphatic system. The prognosis for small cell lung cancer is generally poorer than that for non-small cell lung cancer due to its aggressive nature, but treatment options such as chemotherapy and radiation therapy can help improve survival rates.